1. Technical Field
The present disclosure relates to an optical disc and, more particularly, to a method of controlling a servo in an optical disc device and a servo control device using the same method.
2. Discussion of Related Art
Examples of optical disc devices include compact disc players, laser disc players, and compact disc graphic players. Such optical disc devices are used to reproduce images and/or sounds recorded on an optical disc using a display screen and/or a speaker.
The optical disc devices use light to write and read data to and from an optical disc. For such operations, an optical focus should be accurately placed on a signal surface of the optical disc. Most conventional optical disc devices use servo control devices for achieving accurate focusing. Such a servo control device performs a focus servo operation and a tracking servo operation. In the focus servo operation, an object lens of an optical pickup is moved perpendicularly to an optical disc surface for optical focusing. In the tracking servo operation, the object lens is moved in parallel to the optical disc for optical tracking. For example, in the focus servo operation, focus error signals detected while the object lens is moved perpendicularly to the optical disc can be fed back to minimize focus errors. In the tracking servo operation, tracking error signals detected while the object lens is moved in parallel to the optical disc can be fed back to minimize tracking errors.
According to recently developed technology, a predetermined image can be printed on a label surface of an optical disc for recording desired data. For this, an optical disc device may use a laser diode to write data to the label surface of the optical disc. If the optical disc device is servo-controlled using fed-back focus error signals, however, because a laser beam is accurately focused on the label surface of the optical disc, an excessive thermal concentration can be caused, and thus recorded data can be poorly retained. Moreover, due to the accurate focusing, a recording width of the optical disc can be narrow. In this case, recording time increases.
To address these problems, the distance between an optical disc and an object lens of an optical disc device can be increased. If the optical disc device is servo-controlled using fed-back focus error signals, however, the increase of the distance between the optical disc and the object lens is limited due to the characteristics of the focus error signals. Therefore, what is needed is a method of servo-controlling an optical disc device while allowing an object lens of the optical disc device to move within an increased range.